Recently, as application of magnetic substance, a use for radio wave absorbent attracts attention. For instance, in order to reduce radiation of noise from electronic equipment including cellular phone and computer, the magnetic loss of a magnetic substance is used.
The electromagnetic wave absorbent using the magnetic loss of a magnetic substance is located near a parts as a noise generation source for suppressing the radiation of noise. In this regard, it is known that the radio wave absorption property depends on the magnitude of the imaginary component μ″ of complex magnetic permeability μ=μ′−jμ″ of the magnetic substance, and the larger the magnitude of the imaginary component μ″, the better property the magnetic substance has.
Such an electromagnetic wave absorbent using the magnetic substance includes a compact of mixture of the magnetic substance powder and a resin. For example, in an electromagnetic wave absorbent disclosed in JP-A 2004-128001 (KOKAI), the real component μ′ and the imaginary component μ″ of complex magnetic permeability μ are adjusted to satisfy μ′>μ″ and μ′≧5 in a particular frequency region within a high-frequency region of 1 to 3 GHz. Here, a radio wave absorbent is fabricated by assembling and aggregating many of at least one of (1) a magnetic powder having a chain-like structure of a large number of microspheres and (2) a microsphere magnetic substance powder under a condition that particles are individually insulated by electric insulating materials.
However, in the method, the magnetic substance powder particles are electrically insulated, and it is difficult to obtain a superior radio wave absorption property at a high frequency more than several hundreds of megahertz. Further, since the magnetic anisotropy of the used magnetic particles is small, there is similarly a limit in radio wave absorption at the high frequency.
In addition, in a method for radio wave absorption as shown in JP-A 10-106814 (KOKAI) or the like, flattened magnetic particles are used for providing magnetic anisotropy to the magnetic particles. Accordingly, the method can deal with the higher frequency. However, when the flattened magnetic particles are fabricated, there is a limit in size of the particles. On this account, the radio wave absorption property at a high frequency more than several hundreds of megahertz is low.
Moreover, JP-A 2007-8762 (KOKAI) discloses a magnetic substance better in plasticity because magnetic substance particles have a continuous network structure.